The present invention relates to a magnetoelectric transducer of improved reliability and yield, and to a method of producing a magnetoelectric transducer capable of remarkably reducing the number of process steps required in manufacture.
Magnetoelectric transducers are elements used to convert a change of magnetic field into an electric signal, and are widely used in many applications as magnetic sensors.
A Hall element is used for the magnetoelectric transducer, and mica or ferrite is widely used as the substrate of the magnetoelectric transducer.
The present invention also relates to a Hall element formed with a magneto-sensitive portion and a compensation resistor for restricting any variation of the output voltage of the Hall element due to a change of temperature, these two elements being formed on the same substrate.
FIG. 1 is a schematic sectional view showing one example of a conventional magnetoelectric transducer. In FIG. 1, a base layer 2 is deposited on the surface of a substrate 1, and a semiconductor thin film 3 is formed by crystal growth on the surface of the base layer 2. Further, an electrode thin film 4 is formed on the surface of the semiconductor thin film 3 using mask evaporation such that a portion of the surface of the semiconductor thin film 3 is retained, and a protective film 5 is then formed on the surface of the electrode thin film 4 and the partial surface of the semiconductor thin film 3 using mask evaporation. The peripheral surfaces of the element thus constructed are integrally enveloped by a molding resin 6.
Most conventional magnetoelectric transducers use InSb, according to a method where a single crystal of InSb is sliced to a thickness of about several micrometers, and a pattern is formed by means of an evaporation method using a metal mask, or an etching method. For the electrode thin film 4, Cr, Al, Ag or Au, the combination thereof or a conductive paste is used, and for the protective film 5, SiO.sub.2 or Al.sub.2 O.sub.3 are generally used. These materials are deposited using a CVD or RF sputtering method, and then a pattern is formed by photoetching or mask evaporation using a metal mask.
However in the slicing of single crystal InSb to a thickness of about several .mu.m, it is necessary to repeat mechanical polishing and chemical etching processes and the like, thereby not only making the fabrication thereof complex but also causing variations in the thickness of the thin plate to cause large variations in the characteristics of the element. Further, in the mask evaporation method, the temperature distribution is minutely changed in accordance with the formation of the mask, thereby causing a non-uniform characteristic of the evaporation film, and further, non-uniform characteristics of the element due to distortions in mask formation and the pattern in the evaporation process.
Referring to FIG. 5, an example of a magnetoelectric transducer using a substrate made of mica is shown. In FIG. 5, a semiconductor thin film 22 is formed on the surface of the mica substrate 21, and an electrode thin film 23 is evaporated on a portion of the semiconductor thin film 22 to form a terminal portion. The upper surface of the semiconductor thin film 22 and the electrode thin film 23 thus constructed is coated with a protective film 24, and then the entire assembly is coated with a molding resin 25 to protect the same.
Referring to FIG. 6, the construction of a magnetoelectric transducer using a ferrite substrate 26 is shown. In this magnetoelectric transducer, a film 27 of Al.sub.2 O.sub.3 is deposited on the surface of the ferrite substrate 26; and the semiconductor layer 22, the electrode thin film 23 and the protective film 24 are formed in the manner shown in FIG. 5. On the protective film 24, a collector 28 is provided at approximately the central portion of the semiconductor thin film 22, and the assembly thus constructed is coated with the molding resin 25.
In the FIG. 5 device using the mica substrate, natural mica is cut into a predetermined form and the surface thereof is cleaned, and it is then cleaved to provide a surface for the semiconductor thin film. The semiconductor thin film 22 is then formed by crystalline growth on the cleaned surface of the mica substrate 1 by means of CVD, an evaporation method or the like. The semiconductor thin film thus constructed is processed to form an element pattern by a method of photoetching or evaporation using a pattern mask. The element formed with the electrode thin film 23 and the protective thin film 24 is cut for each element, and each element is coated with the molding resin 25.
In the magnetoelectric transducer using the ferrite substrate, the above-mentioned manufacturing processes are similarly applied, but the Al.sub.2 O.sub.3 film is provided on the ferrite substrate in order to facilitate the crystalline growth of the semiconductor thin film, and further, the collector 28 is provided on the semiconductor thin film 23 through the protective film 24 in order to increase the sensitivity thereof.
In the magnetoelectric transducer using the mica substrate, good matching in the crystalline growth of InSb or InAs semiconductor thin films can be obtained, so that carrier mobility of 60,000 cm.sup.2 /V sec can be obtained. On the other hand, discontinuity of the evaporated film is caused by a cleavage of the mica, thereby reducing its reliability. Further, upon cutting and separation of each element, cleavage of the mica substrate is undesirably caused thereby reducing the yield. In the magnetoelectric transducer using the ferrite substrate, good matching to the crystalline growth cannot be obtained, so that it is inevitably necessary to increase the sensitivity by sandwiching the semiconductor thin film with high magnetic permeability materials such as ferrite, permalloy and the like, resulting in a complex construction. Further, since the collector is mounted on the upper portion of the semiconductor thin film, the collector is affected by an external force from the molding resin to thereby apply stress to the semiconductive thin film. The semiconductor thin film is thus affected with distortion resistance to thereby produce voltage deviations, which result in a low stability of the element. Further, the ferrite substrate has low heat conductivity, so that the temperature of the element is increased, thereby to reduce the sensivity.
Under this circumstance, one might use a ceramic substrate in order to eliminate the heat problem, however, it is difficult to obtain a large sized substrate because of the difficulty of mirror surface polishing.